The present invention relates to a packet transmission router to be used for a VRRP (Virtual Router Redundancy Protocol) network having a VR (Virtual Router) function.
The VRRP is the technology for improving the reliability of the packet transmission router used in the network. In the VRRP, a packet transmission router is physically composed of a plurality of packet transmission routers for redundancy so that even if a single one of those routers fails, the other ones can take over the process from the damaged router to keep the operation of the whole packet transmission router not stopped. The router that is now processing packets is called the active packet transmission router, and the spare router that operates when the active router fails is called the standby packet transmission router.
FIG. 1 shows an example of the packet transmission router having the VRRP function incorporated. As illustrated in FIG. 1, the nodes 1˜8 provided on the network are connected through the packet transmission routers (that is, packet transmission routers 1, 2). The packet transmission router 1 serves as the active packet transmission router, and the packet transmission router 2 as the standby packet transmission router. The packet transmission routers are numbered 1, 2 as identifiers (VRID), respectively. Each of the nodes recognizes the packet transmission router 1 as the active packet transmission router so that data can be always transmitted to the packet transmission router 1. The packet transmission router 1 as the active packet transmission router generates a VRRP packet so that the VRRP packet can be periodically transmitted to the packet transmission router 2, or the standby packet transmission router. The packet transmission router 2 confirms from the VRRP packet that there is the packet transmission router 1 and that the VRID is 1.
If the router 1 goes down due to any disorder, the router 2 that consequentially cannot receive the periodical VRRP packet recognizes that there is no longer the router 1, and changes its own IP address and MAC address to those of router 1. Therefore, even if the router 1 fails, the router 2 takes over the IP address and MAC address of the router 1, and thus data can be continuously transferred to be seamless with ARP (Address Resolution Protocol) table not restructured.
FIG. 2 shows the format of the VRRP packet. Referring to FIG. 2, the version of VRRP is stored in the “VERSION” field. 1 is stored in the “TYPE” field. All packets having any number except 1 are discarded. The VRID value is stored in the “VRRP IDENTIFIER” field. The VRID enables the active and standby packet transmission routers to identify the relationship between themselves. A value of 0˜255 is stored in the “PRIORITY” so that the routers that transmit packets of larger priority values can be selected as active routers. A value of 0˜255 is stored in the “ADVERTISEMENT INTERVAL”, making it possible to specify the transmission interval of VRRP packets. In the “IP ADDRESS” is stored the IP address of the active router, or the IP address shared on the VRRP network. The VRRP packet generated is capsulated with a data link header and IP header and transferred.
There is another technology called VR (Virtual Router) that logically builds up a function to serve as a plurality of packet transmission routers on a single packet router. The term VR is the technology in which the presence of a plurality of packet transmission routers is emulated on a certain physical packet transmission router on a software basis. The virtual packet transmission routers thus emulated are called VR (Virtual Router). The VR is regarded as an elemental technology that is important to realize virtual closed networks on the Internet.
FIG. 3 is a conceptual diagram of the virtual router. A packet transmission router 11 shown in FIG. 3 is physically a single router, but has two routers VR 1, VR 2 on a software basis. As illustrated in FIG. 3, the packet transmission router 11 in which the virtual routers VR 1, VR 2 operate is connected to ISP (Internet Service Provider) 1 and ISP 2 so that packets between ISP1 networks can be transmitted and received through VR1 and packets between ISP2 networks can be transmitted and received through VR2. The virtual routers VR 1, VR 2 respectively manage their own routing tables associated with ISP 1, ISP 2. For example, only information within provider ISP 1 is stored in the routing table that router VR 1 manages so that the network interface to transmit to can be discriminated by referring to the destination address of the received packet. In most cases, in order to economize the memory space for storing the routing tables, a single routing table is actually shared by the routers VR 1, VR 2, but the routers VR 1, VR 2 respectively manage only entry tables for reference to the routing table. The packet sent to node 1 is transmitted through a network interface 31. Therefore, even if the nodes 1, 3 had the same IP address, information to be sent to node 1 could not be transmitted through a network interface 32 or information to be sent to node 3 could not be transmitted through the network interface 31.